1. Field of the Invention
The present invention relates to steering wheels for vehicles.
2. Description of the Related Art
A typical steering wheel includes an annular gripping ring and a pad. The pad is located at the center of the ring and connected to the ring by spokes. A metal ring core is embedded in the ring while a metal spoke core is embedded in each spoke. The ring core and the spoke cores are covered with a surface layer made of polyurethane foam, or the like. The spoke cores are coupled to a boss plate located below the pad. The boss plate is fixed to an end of a steering shaft.
To assemble such a steering wheel, the boss plate is first fixed to the steering shaft. An air bag device is then mounted on the boss plate. The air bag device is covered by the pad.
When the steering wheel receives a load that is greater than a predetermined level, the spoke cores deform and allow the entire steering wheel to be displaced downward and toward the end of the steering shaft. This absorbs and decreases the load applied to the steering wheel.
Japanese Unexamined Utility Model Publication No. 2-133955 describes a steering wheel having a surface layer and a pad that are formed integrally. This structure eliminates slight gaps between the layer and the pad and thus improves the appearance of the steering wheel. Such a steering wheel also needs a mechanism for absorbing and decreasing load that acts thereon.
In the steering wheel having an integral pad and surface layer, the air bag device is coupled to the spoke cores. Thus, when the steering wheel receives a load that is greater than a predetermined level, the air bag device is displaced downward together with the spoke cores. However, if the space between the air bag device and the boss plate is small, the boss plate restricts the movement of the air bag device. This reduces marginal space that is necessary to allow deformation of the spoke cores. As a result, this may lead to insufficient absorption of the load applied to the steering wheel.
In order to solve the above problem, the distance between the air bag device and the boss plate may be enlarged to increase the marginal space that allows deformation of the spoke cores. This would allow a further downward displacement of the spoke cores and the air bag device. However, the increased distance between the air bag device and the boss plate increases the axial thickness of the steering wheel. This enlarges the steering wheel.